Probe-holder armatures are a means whereby a measuring probe that is in most cases of a standardized design can be installed and/or uninstalled in a simple manner for example in a chemical, pharmaceutical or biological process or in a container in which such a process takes place. It can become necessary to remove a measuring probe from a process for example in order to exchange a defective measuring probe, or in order to protect the measuring probe for example when the process system is being cleaned. The known types of holder armatures for interchangeable probes are therefore in many cases equipped with a treatment chamber in which the measuring probe can be, among other things, cleaned, subjected to a function test, and/or calibrated in separation from the process apparatus. Holder armatures for interchangeable probes are used for example together with different measuring probes, such as pH probes, conductivity probes, ion-sensitive probes, turbidity-measuring probes, or gas probes, among others.
Holder armatures for interchangeable probes of the known types are designed in a substantially cylindrical shape. A measuring probe is inserted into the holder armature from the end that faces away from the measurement medium, so that a cable that is connected to the measuring probe will exit at that end from the armature. In the exchange of the measuring probe, it can happen that the latter is simply pulled out of the holder armature by the probe cable, whereby the cable can in some cases be forcibly separated from the measuring probe. In addition, the cable can also be stressed by a pulling force during operation of the armature, whereby the connection between the cable and the measuring probe can be weakened.
In view of the conditions that holder armatures for interchangeable probes are exposed to in chemical processes, the design of the armatures has to be very much safety-oriented, so as to prevent the possibility that the measuring probe is inadvertently removed from the holder armature.
The applicant's European patent application EP 0 882 896 A1 discloses a holder armature for interchangeable probes in which a measuring probe is arranged in an immersion tube in a way that allows the probe to be taken out of the tube. The immersion tube is arranged in a housing in which the tube is axially movable between a rest position and a measuring position. Between the immersion tube and the measuring probe that is arranged inside it, there is at least one seal which seals the immersion tube against the measurement medium. This holder armature comprises a locking element which prevents axial movement of the immersion tube when no measuring probe is in place.
A holder armature for interchangeable probes which has a treatment chamber and a locking element against inadvertent removal of the measuring probe is disclosed in applicant's U.S. patent application, which is co-pending as U.S. Ser. No. 11/075,483 and which has been published as US 2005/0229727 A1. This holder armature is likewise designed so that the measuring probe is inserted from the end of the holder armature that is farther from the measurement medium into the immersion tube that is located inside the holder armature. As a locking element, the immersion tube has an insert which can be fixedly secured, whereby the measuring probe is pushed against a stop which is located inside the immersion tube and directed towards the measurement medium.
In spite of the safety measures that are known at this state of the art, it would certainly still be possible in principle to pull the measuring probe from the holder armature with brute force, even if the immersion tube is in the measuring position. This would have the consequence that the measurement medium could enter into the holder armature and also escape from there into the environment, a risk which especially with aggressive and/or toxic media must be avoided under all circumstances.
State-of-the-art holder armatures for interchangeable measuring probes have an immersion tube which is axially movable in a housing and in which the measuring probe can be arranged. This immersion tube is matched at least to the length of the measuring probe. The length of the immersion tube often determines the maximum outside height of the holder armature, i.e. the height of the part of the armature that is on the outside of the container. Especially when long sensor probes are used, the immersion tube can protrude in its rest position from the holder armature or from the housing of the latter at the end that points away from the measurement medium. When changing from the rest position into a measuring position, the immersion tube together with the measuring probe arranged inside it is moved axially in the housing in the direction towards the measurement medium. The installation height of the state-of-the-art holder armatures for interchangeable probes therefore varies depending on where the immersion tube is positioned within its displacement range and depending on the measuring probe that can be arranged in the immersion tube. The installation height needs to be considered especially in the design of process systems in order to provide enough clear space to allow the removal of the measuring probe from the holder armature. The holder armature should preferably be integrated in the system in such a way that the armature is easily accessible, but that the change of the outside height when the immersion tube is moved to a different position does not pose a danger to parts of the process system, to nearby objects, or even to persons that may be present in the vicinity.
The invention therefore has the objective to propose an improved design for a holder armature for interchangeable measuring probes, which is in particular safe to operate, and which overcomes the drawbacks described above.